The present invention relates to an improved angular position sensor, which will not suffer damage as result of differential vibration between a rotating shaft and a housing.
An angular position sensor detects the angular orientation of a rotating shaft with respect to a housing. It may be desirable, for example, to know exactly when a rotating shaft is in a given angular orientation and therefore it is desirable to monitor the angular orientation of a shaft as it rotates about its longitudinal axis.
In the immediate proximity of a bearing, a rotating shaft will exhibit little radial vibration. Along a length of shaft between spaced bearings, however, a rotating shaft will endure a certain amount of radial vibration, or differential vibration, because the shaft is not perfectly symmetric about its longitudinal axis and the bearings positioned along the length of a shaft are not perfectly aligned with the axis of the shaft.
Existing angular positioned sensors consist of a rotor which fits around the circumference of the shaft and includes a brush which engages an annular resistive contact mounted on a stationary member. An electrical potential is applied across the resistive member and the brush and the current through the resistive member is measured to provide a reading of the angular orientation of the brush with respect to the resistive member.
To accommodate for differential vibration, the stationary member is configured as a clamshell loosely assembled around the rotor with the stationary clamshell mounted to the housing through which the shaft passes. As a result of the forgoing, the rotor can vibrate with the shaft and within the stationary clamshell. Currently, the parts of the angular position sensor, including the rotor and the clamshell, are made of plastic and the differential vibration of the plastic rotor within the clamshell results in contact between the rotor and clamshell housing. The friction that occurs as portions of the spinning rotor contact the clam shell causes fine particles of plastic to be tossed within the interior of the clam shell and the particles of plastic ultimately create interference between the brushes and the resistive surfaces on the stationary member. The interference between the contacts of the brushes and the annular resistive substrate causes the device to produce inaccurate angular position readings. It would be desirable, therefore, to provide an improved angular position sensor having parts that would not vibrate against each other while the rotor is rotating with a shaft.
Briefly, the present invention is embodied in an angular position sensing device for determining the angular orientation of a shaft rotatable with respect to a housing body. The sensor includes a rotor having a bore sized to receive the shaft and means for locking the rotor for rotation with the shaft. The rotor also has an annular male bearing surface.
The device further includes a first rotor housing having an annular female bearing surface complementary to the annular male bearing surface of the rotor. The female bearing surface of the first rotor housing is in engagement with the male bearing surface of the rotor thereby allowing the rotor to freely rotate within the first rotor housing while the first rotor housing vibrates with the rotor and the shaft.
Like prior art angular position sensors, a sensor in accordance with the present invention has an annular resistive substrate on one of the rotor and the rotor housing and a brush on the other of the rotor and the rotor housing. The brush is in engagement with the resistive substrate such that the angular orientation of the brush with respect to the rotor housing may be measured by applying a potential across the substrate and the brush and measuring the changes that occur in the current passing through the parts.
In accordance with the invention to permit the rotor to vibrate with respect to the housing supporting the shaft, the position sensor of the present invention includes a second housing that surrounds the rotor housing. A plurality of spring members extend between the first rotor housing and the second rotor housing for moveably retaining the first rotor housing, with the rotor therein, with respect to the second rotor housing. In a second embodiment an annular gasket is fitted between the outer circumference of the inner housing and the inner circumference of the outer housing to permit movement of the inner housing with respect to the outer housing.